MAX16826 Datasheet, PDF(20/26 Page) Maxim Integrated Products – Programmable, Four-String HB LED Driver with Output-Voltage Optimization and Fault Detection

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MAX16826 Datasheet, PDF (20/26 Pages) Maxim Integrated Products – Programmable, Four-String HB LED Driver with Output-Voltage Optimization and Fault Detection

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Programmable, Four-String HB LED Driver with

Output-Voltage Optimization and Fault Detection

The register file unit is used to store all the control infor-

mation from the SDA line and configure the MAX16826

for different operating conditions. The register file

assignments of the MAX16826 are in Table 2.

Registers 00h to 03h: String Current Programming

These registers are used to program LED string 1 to

LED string 4 current sink values. For each LED string,

CS1âCS4 inputs are connected to the source of the

external current sink FET and internally are connected

to the inverting input of the internal transconductance

amplifier. The noninverting input of this amplifier is con-

nected to the output of an internal DAC programmed

by these registers. As the DAC is incremented, its out-

put voltage decreases from 316mV to 97mV in 1.72mV

steps by the data written in the register 00h to 03h;

thus, the steady-state voltage at CS1âCS4 is given by

the following formula:

VCS1,2,3,4 = 316mV - (1.72mV x RegisterValue[6:0])

For example, if 00h is set to 20h, then the CS1 voltage is:

VCS1 = 316mV - 1.72mV x 32 = 265.3mV

Output Programming

Set the switching regulator output voltage by connect-

ing FB to the center of a resistive voltage-divider

between the switching regulator output and GND. VFB

is regulated to a voltage from 876mV to 1.25V (typ) set

by the register 04h through the I2C interface.

The FB reference voltage can be decreased from 1.25V,

its maximum value, by approximately 2.9mV steps. The

steady-state voltage at FB then is regulated to:

VFB = 1.25V - (2.91mV x 04h[6:0])

Registers 05h to 08h: External Current-Sink

FET Drain Voltage ADC Readings

These registers store the drain voltages of the external

current sink FETs. For each register, bits 6â0 are the

conversion data of the ADC outputs. Bit 7 is used to

show if the conversion is terminated by the ADC (indi-

cated by 0) or if there is an internal timeout (indicated

by 1). If the drain voltage exceeds the preset reference

voltage, the corresponding LED string fault bit is assert-

ed. See the Faults and Fault Detection section for more

information on the internal timeout function.

Voltage ADC Output

Bits 6-0 of this register store the voltage present at

OVP. This voltage is a scaled down version of the

switching regulator output voltage. Bit 7 is not used.

This register stores all the external events or fault infor-

mation such as overvoltage and shorted LED string

faults. The fault events are logged only if the system is

not in standby mode and their active states are longer

than one clock cycle. Cycle enable or power to clear the

fault status register. Initiating standby mode using the

I2C interface can also be used to clear the fault status

Table 2. Register File Assignments

ADDRESS

R/W

00h

R/W

01h

R/W

02h

R/W

03h

R/W

04h

R/W

05h

06h

07h

08h

09h

0Ah

0Bh

R/W

0Ch

USED BIT

RANGE

[6:0]

[7:0]

[6:0]

[5:0]

[0]

[2:0]

RESET

VALUE

00h

DESCRIPTION

LED String 1 current programming value.

LED String 2 current programming value.

LED String 3 current programming value.

LED String 4 current programming value.

Switching regulator output voltage programming value.

LED String 1 external FET drain voltage ADC output.

LED String 2 external FET drain voltage ADC output.

LED String 3 external FET drain voltage ADC output.

LED String 4 external FET drain voltage ADC output.

OVP voltage, ADC output.

Fault status register.

Device standby command.

Device revision code.

20 ______________________________________________________________________________________

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